The invention relates generally to control of compression-ignition engines, and more particularly to cam sensor elimination in four stroke compression-ignition engines having cylinders with large displacement volumes, such as locomotive or marine type engines.
Although various techniques for eliminating cam sensors have been provided in the context of relatively small spark-ignition engines, these type of techniques are believed not to be suited to the unique designs of larger compression-ignition engines, such as diesel engines. For example, the single cylinder displacement for a large sixteen cylinder locomotive diesel engine may be on the order of 11 liters whereas the single cylinder displacement for a typical diesel truck may be on the order of only 2 liters per cylinder. Therefore a single cylinder for a large locomotive engine may easily be more than five times larger than that of a large diesel truck. In addition, a typical truck engine has 6 or 8 cylinders as opposed to 12 or 16 for a typical locomotive engine, thus each cylinder contributes a smaller portion of the total power. This generally translates into very different design constraints since high injection pressure levels (on the order of 10-20 k.p.s.i.) are required in conjunction with much higher volume fuel flow rate ranges (100-1600 mm3/stroke) to effectuate proper combustion in the larger locomotive engine.
Other differences also impact the type of fuel injection system which may be employed on larger compression ignition engines. For example, locomotive engines are typically designed to maintain governor stability e.g., provide a relatively constant speed output to provide a steady power generating source for large fraction motors used to propel the wheels. Also, large locomotive engines encounter radical load changes due to switching of large auxiliary loads such as compressor loads, fan loads, and “hotel” power loads (an alternator for generating 110 V at 60 Hz) for passenger train applications. Driving such loads or turning off such loads can result in load changes on the order of 500 horsepower at any instant.
Another design consideration generally unique to such larger engines is lower engine speeds (RPM) and reduced chamber air movement. Smaller engines typically operate at engine speeds of several thousand RPM's. However, larger locomotive engines typically operate at between 0-1050 RPM. The rate at which the pistons move generally impacts the air intake speed and/or swirl. Lower RPM typically translates into slower air intake. With smaller volume cylinders, sufficient chamber air movement to allow proper atomization of the fuel to air mixture typically occurs during the power stroke. However, larger cylinders typically have much less cylinder air movement which results in a more stagnant trapped air volume. This generally requires a greater fuel injection pressure to be applied to overcome the in-cylinder compression and penetrate the trapped air volume in a sufficiently atomized state, such that entrainment will result in a homogenous and stoichiometric bum of the air/fuel mixture.
In a conventional locomotive engine design, a crank sensor synchronizes an engine governor unit (EGU) to the crank. A cam sensor, however, determines the respective stroke the engine is actually in, that is, without the cam sensor, the EGU would not be able to determine the difference between a compression stroke and an exhaust stroke. Once the cam position is known, the EGU does not typically need additional cam data because by sensing crank teeth information, the EGU is able to maintain the proper cam sense. Presently, one simply cannot start the locomotive engine without the cam sensor.
In view of the above-discussed issues, it would be desirable to provide control techniques that would allow for reliably providing controlled start of the compression-ignition engine of the locomotive even in the absence of the cam sensor since, presently, the cam sensor is a single point failure in the locomotive. Another reliability enhancement resulting from the elimination of the cam sensor would be to eliminate loss of synchronization in the EGU due to noisy cam pulses. It would be further desirable to lower manufacturing costs of the engine since if one could eliminate the cam sensor, one could also eliminate machining done on the cam sensor cover and timing wheel. Further, wiring and circuitry on the EGU that processes the cam sensor signal could be eliminated. Additionally, elimination of the cam sensor would result in a simpler manufacturing process not requiring time consuming and error prone cam sensor gapping actions.